package servlet;

import pojo.User;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;

@WebServlet(urlPatterns = {"/user"})//注解，确定请求地址，（一个类只能响应一个请求）
public class UserHelloServlet extends HttpServlet {//类继承HttpServlet才能响应
    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //System.out.println("进入后台");
        List<User> users=new ArrayList<>();//集合,保存数据
        //jdbc操作数据库 查询
            //1.加载驱动
            try {
                Class.forName("com.mysql.cj.jdbc.Driver");
                //2.获取连接(url username password)
                String url = "jdbc:mysql://127.0.0.1:3306/jdbc?characterEncoding=utf-8";
                Connection connection = DriverManager.getConnection(url, "root", "526874");
//            if (connection!=null){
//                System.out.println("连接成功");
//            }
                //3.写sql
                String sql = "select * from t1";
                //4.预编译sql
                PreparedStatement preparedStatement = connection.prepareStatement(sql);
                //5.有参数设置参数
                //6.执行sql
                ResultSet resultSet = preparedStatement.executeQuery();
                //7.遍历结果集
                while (resultSet.next()) {
                    User user = new User();
                    user.setId(resultSet.getInt(1));
                    user.setName(resultSet.getString(2));
                    user.setPass(resultSet.getString(3));
                    //把对象添加到集合中
                    users.add(user);

                }
                //8.关闭资源
                resultSet.close();
                preparedStatement.close();
                connection.close();

                //把集合中数据存储到作用域中
                req.setAttribute("users",users);//(key,value)
                //打开页面
                req.getRequestDispatcher("/user.jsp").forward(req,resp);

            } catch (ClassNotFoundException e) {
                throw new RuntimeException(e);
            } catch (SQLException e) {
                throw new RuntimeException(e);
            }
        }
}
